Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $215.39   7.849%   $232.296   $232.30   $232.30   $232.30  
  Purchase #2 $24.75   9.187%   $27.0238   $27.02   $27.00   $27.00  
  Purchase #3 $65.31   3.667%   $67.7049   $67.70   $67.70   $67.70  
  Purchase #4 $152.36   9.843%   $167.3568   $167.36   $167.35   $167.40  
  Purchase #5 $170.46   3.761%   $176.871   $176.87   $176.85   $176.90  
  Purchase #6 $163.76   13.251%   $185.4598   $185.46   $185.45   $185.50  
  Purchase #7 $63.70   8.366%   $69.0291   $69.03   $69.05   $69.00  
  7 purchase totals = $855.73       $925.7414   $925.74   $925.70   $925.80